Here is another interesting study from the good people at Redox Report:

Changes of markers of oxidative stress during menstrual cycle
Authors: Karowicz-Bilinska, Agata1; Plodzidym, Magdalena2; Krol, Joanna2; Lewinska, Anna2; Bartosz, Grzegorz3
Source: Redox Report, Volume 13, Number 5, October 2008 , pp. 237-240(4)

Abstract:
The levels of urinary hydrogen peroxide and thiobarbituric acid reactive substances have been compared during the menstrual cycle of 12 regularly menstruating women. Higher level of both indices of oxidative stress (normalized with respect to creatinine content) were found in the luteal phase of the cycle. These results give further evidence for the usefulness of urinary hydrogen peroxide and thiobarbituric acid reactive substances as potential biomarkers of oxidative stress and for the antioxidant action of estrogens.